1. Field of the Invention
The present invention relates to a driving technique for driving an actuator having a shape memory alloy and giving a displacement to a movable part on the basis of a displacement target value.
2. Description of the Background Art
A shape memory alloy (hereinafter, also referred to as “SMA”) has a property such that even if it is plastic-deformed by an external force at a temperature equal to or less than a martensite transformation start temperature, when heated to a temperature equal to or more than a reverse transformation end temperature, the SMA regains its memorized original shape. There has been known a technique using an SMA having such a property for an actuator.
A technique using the SMA is disclosed in, for example, Japanese Patent Application Laid-Open No. 2003-111458. According to the technique, in two SMAs connected in a push-pull configuration to a movable part which can be moved in the horizontal direction, no current is passed to the SMA that radiates heat and expands, and current is passed only to the SMA to be heated and contracted, thereby driving the movable part.
In the driving technique of Japanese Patent Application Laid-Open No. 2003-111458, however, no current is passed to the SMA on the heat radiation side so that, in some cases, the SMA is cooled excessively. In such a case, to heat the excessively cooled SMA and make it contracted, time to heat the SMA to the reverse transformation start temperature causes a response delay. Consequently, it is difficult to apply the driving technique to a system requiring high response.